This invention relates to an information recording medium on which information can be recorded by means of a laser beam having a high energy density, and a dye compound which is favorably utilized for preparing the information recording medium.
The recordable compact disc (CD-R), on which information can be recorded only once, is widely used, for instance, as a large capacity computer data disc.
The optical disc of CD-R type generally comprises a disc-shaped substrate (support) and a recording layer provided thereon. The disc substrate comprises a transparent material such as synthetic resin. The recording layer comprises a metal or a semi-metal such as Bi, Sn, In or Te, or alternatively a dye such as a cyanine dye, a metal-complex dye, or a quinone dye. A light-reflecting layer and a protective layer may be superposed in order on the recording layer. The light-reflecting layer and the protective layer can be made of gold and resin, respectively.
On the CD-R, the writing (recording) and reading (reproducing) can be performed in the following manner. The laser beam (usually used wavelength is 780 nm) modulated by information is applied to the recording layer of the CD-R through the substrate. The recording layer alters its optical characteristics in the area where the laser beam has been applied, to produce a chemical or physical change such as production of pit. The reading of the recorded information can be performed by sequentially applying a laser beam on the recording layer of the CD-R through the substrate and detecting a light reflected on the CD-R.
At present, most of the recording layer of CD-R utilizes a light-sensitive dye as the recording material, because the recording dye layer can be easily formed by a coating method and shows a high sensitivity, as compared with the recording metal layer. However, the dye layer has such disadvantages as low light-resistance and low heat resistance. Therefore, it has been desired to develop a recording layer having high durability against light and heat, as well as having high recording and reproducing characteristics.
Japanese Patent Provisional Publication No. 63-209995 describes an optical disc which has a recording layer comprising an oxonol dye. According to the description of publication, such optical disc maintains stable recording and reproducing characteristics for a long time. The publication discloses an oxonol dye compound having an ammonium ion in the form of an inner salt.
The inventors have found that the optical disc having the recording layer of the above oxonol dye exhibits insufficient light-resistance, while the disc has relatively improved characteristics in view of heat resistance and durability for repeated reproducing. Therefore, such optical disc often causes troubles in reproducing process after long exposure to light such as sunlight.
Accordingly, it is an object of the present invention to provide an information recording medium having stable recording characteristics and particularly high light-resistance to maintain satisfactory recording characteristics for a long time.
It is another object of the present invention to provide a new oxonol dye compound favorably employable for preparing the information recording medium having stable recording characteristics.
The present invention resides in an information recording medium comprising a support and a recording layer provided thereon on which information can be recorded by means of a laser beam, wherein said recording layer contains a dye compound having the below-mentioned formula (I-1) or (I-2): 
in which each of A1, A2, B1 and B2 independently represents a substituent group; each of Y1 and Z1 independently represents a group of atoms required for forming a carbon ring or a heterocyclic ring; each of E and G independently represents a group of atoms required for forming a conjugated double bond chain; X1 represents xe2x95x90O, xe2x95x90NR or xe2x95x90C(CN)2, wherein R is a substituent group; X2 represents xe2x80x94O, xe2x80x94NR or xe2x80x94C(CN)2, wherein R is a substituent-group; each of L1, L2, L3, L4 and L5 independently represents a methine group which may have a substituent group; Mk+ represents an onium ion containing a positively charged onium atom to which no hydrogen atom is attached; each of m and n independently is an integer of 0, 1 or 2; each of x and y independently is an integer of 0 or 1; and k is an integer of 1 to 10.
The invention further resides in a new oxonol compound having the below-mentioned formula (IV-1) or (IV-2): 
in which each of A3, A4, B3 and B4 independently represents a substituent group selected from the group consisting of a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, an alkynyl group having 2 to 18 carbon atoms, an aryl group having 6 to 18 carbon atoms, an aralkyl group having 7 to 18 carbon atoms, an acyl group having 2 to 18 carbon atoms, an alkylsulfonyl group having 1 to 18 carbon atoms, an arylsulfonyl group having 6 to 18 carbon atoms, an alkylsulfinyl group having 1 to 18 carbon atoms, an alkoxycarbonyl group having 2to 18 carbon atoms, an aryloxycarbonyl group having 7 to 18 carbon atoms; an alkoxy group having 1 to 18 carbon atoms, an aryloxy group having 6 to 18 carbon atoms, an alkylthio group having 1 to 18 carbon atoms, an arylthio group having 6 to 10 carbon atoms, an acyloxy group having 2 to 18 carbon atoms, a sulfonyloxy group, a carbamoyloxy group, an amino group, a carbamoyl group, a sulfamoyl group, a halogen atom, a hydroxyl group, a nitro group, a cyano group, a carboxyl group, and a 4- to 7-membered heterocyclic group, wherein these substituent groups may be substituted with at least one group selected from those consisting of the above-mentioned substituent groups;
each of Y2 and Z2 independently represents a group of atoms required for forming a 4- to 7-membered carbon ring or a 4- to 7-membered heterocyclic ring, which may be substituted with at least one group selected from those consisting of the substituent groups described for A3, A4, B3 and B4 and may be fused with a 4- to 7-membered carbon ring or a 4- to 7-membered heterocyclic ring;
each of L6, L7, L8, L9 and L10 independently represents a methine group which may have one or two substituent groups selected from the group consisting of the substituent groups described for A3, A4, B3 and B4;
M2+ represents a quaternary ammonium ion; and
each of m1 and n1 independently represents an integer of 0, 1 or 2.
In contrast to the known oxonol dye compounds, the new oxonol dye compound of the invention comprises an onium salt in which an onium atom has no hydrogen atoms thereon (quaternary ammonium salt is particularly preferred). The inventors have found that the new oxonol dye compound enhances light-resistance to provide the information recording medium.
The preferred embodiments of the invention are as follows:
(1) Mk+ in the formula (I-1) or (I-2) is a quaternary ammonium ion.
(2) k in the formula (I-1) or (I-2) is an integer of 0 to 4.
(3) k in the formula (I-1) or (I-2) is 2.
(4) Mk+ is an onium ion of the below-mentioned formula (II): 
in which each of R1 and R2 independently represents a group selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a heterocyclic group; each of R3 and R4 independently represents a substituent group; or each set of R1 and R3, R2 and R4, or R3 and R4 can be combined to form a ring; each of q1 and r1 independently is an integer of 0 to 4; provided that plural R3 and plural R4 are the same as or different from each other in the case that q1 and r1 are 2 or more, respectively.
(5) Mk+ is an onium ion of the below-mentioned formula (III): 
in which each of R5 and R6 independently represents a group selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an aryl group and a heterocyclic group; each of R7 and R8 independently represents a substituent group; or each set of R5 and R6, R5 and R7, R6 and R8, or R7 and R8 can be combined to form a ring; each of q2 and r2 independently is an integer of 0 to 4; provided that plural R7 and plural R8 are the same as or different from each other in the case that q2 and r2 are 2 or more, respectively.
(6) In the formula (I-1) or (I-2), each of m and n is 1; m is 0, while n is 2; or m is 2, while n is 2.
(7) In the formula (I-1) or (I-2), X1 is xe2x95x90O and X2 is xe2x80x94O.
(8) A light-reflecting layer is provided on the recording layer.
(9) A protective layer is provided on the light-reflecting layer.
(10) M2+in the formula (IV-1) or (IV-2) is an ion having the below-mentioned formula (V): 
in which each of R11 and R12 independently represents a group selected from the group consisting of an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, an alkynyl group having 2 to 18 carbon atoms, and an aryl group having 6 to 18 carbon atoms, wherein the alkyl, alkenyl, alkynyl and aryl group may be substituted with one or more groups selected from the group consisting of the substituent groups described for A3, A4, B3 and B4 of the formulas (IV-1) or (IV-2); each of R13 and R14 independently represents a substituent group selected from the group consisting of the substituent groups described for A3, A4, B3 and B4 of the formulas (IV-1) or (IV-2); or each set of R11 and R13, R12 and R14, or R13 and R14 can be combined to form a 4- to 7-membered ring; each of q3 and r3 independently is an integer of 0 to 4; provided that plural R13 and plural R14 are the same as or different from each other in the case that q3 and r3 are 2 or-more, respectively.
(11) M2+ in the formula (IV-1) or (IV-2) is an ion having the below-mentioned formula (VI): 
in which each of R15 and R16 independently represents a group selected from the group consisting of an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, an alkynyl group having 2 to 18 carbon atoms, and an aryl group having 6 to 18 carbon atoms, wherein the alkyl, alkenyl, alkynyl and aryl group may be substituted with one or more groups selected from the group consisting of the substituent groups described for A3, A4, B3 and B4 of the formulas (IV-1) or (IV-2); each of R17 and R18 independently represents a substituent group selected from the group consisting of the substituent groups described for A3, A4, B3 and B4 of the formulas (IV-1) or (IV-2); or each set of R15 and R16, R15 and R17, R16 and R18, or R17 and R18 can be combined to form a 4- to 7-membered ring; each of q4 and r4 independently is an integer of 0 to 4; provided that plural R17 and plural R18 are the same as or different from each other in the case that q4 and r4 are 2 or more, respectively.
(12) In the formula (IV-1) or (IV-2), each of m1 and n1 is 1; m1 is 0, while n1 is 2; or m1 is 2, while n1 is 0.
(13) In the formula (IV-1) or (IV-2), each of the carbon ring and the heterocyclic ring for the group of atoms represented by Y2 or Z2 is pyrazolone ring, ring of thiobarbituric acid, ring of barbituric acid, indandione ring, or hydroxyphenalenone ring.
The information recording medium of the invention and the new oxonol compound are further described below.
The information recording medium of the invention is characterized by comprising the recording layer containing the oxonol dye compound having the aforementioned formula (I-1) or (I-2).
The oxonol dye compound of the invention is described below in more detail.
The oxonol dye compound favorably employable for the invention consists essentially of an anion part (dye component) and a cation part (onium component).
First, the anion part is described.
Examples of the substituent groups represented by A1, A2, B1 and B2 in the above formulas include following groups:
an alkyl group of 1-18 (preferably 1-8) carbon atoms which may have one or more substituent groups and which may form straight-chain or branched-chain or cyclic structure (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, cyclohexyl, methoxyethyl, ethoxycarbonylethyl, cyanoethyl, diethylaminoethyl, hydroxyethyl, chloroethyl, acetoxyethyl, and trifluoromethyl);
an aralkyl group of 7-18 (preferably 7-12) carbon atoms which may have one or more substituent groups (e.g., benzyl, and carboxybenzyl);
an alkenyl group of 2-18 (preferably 2-8) carbon atoms (e.g., vinyl);
an alkynyl group of 2-18 (preferably 2-8) carbon atoms (e.g., ethynyl);
an aryl group of 6-18 (preferably 6-10) carbon atoms which may have one or more substituent groups (e.g., phenyl, 4-methylphenyl, 4-methoxyphenyl, 4-carboxyphenyl, and 3,5-dicarboxyphenyl);
an acyl group of 2-18 (preferably 2-8) carbon atoms which may have one or more substituent groups (e.g., acetyl, propionyl, butanoyl, and chloroacetyl);
an alkylsulfonyl or arylsulfonyl group of 1-18 (preferably 1-8) carbon atoms which may have one or more substituent groups (e.g., methanesulfonyl and p-toluenesulfonyl);
an alkylsulfinyl group of 1-18 (preferably 1-8) carbon atoms (e.g., methanesulfinyl, ethanesulfinyl, and octanesulfinyl);
an alkoxycarbonyl group of 2-18 (preferably 2-8) carbon atoms (e.g., methoxycarbonyl, and ethoxycarbonyl);
an aryloxycarbonyl group of 7-18 (preferably 7-12) carbon atoms (e.g., phenoxycarbonyl, 4-methylphenoxycarbonyl, and 4-methoxyphenylcarbonyl);
an alkoxy group of 1-18 (preferably 1-8) carbon atoms which may have one or more substituent groups (e.g., methoxy, ethoxy, b-butoxy, and methoxyethoxy);
an aryloxy group of 6-18 (preferably 6-10) carbon atoms which may have one or more substituent groups (e.g., phenoxy and 4-methoxyphenoxy);
an alkylthio group of 1-18 (preferably 1-8) carbon atoms (e.g., methylthio and ethylthio);
an arylthio group of 6-10 carbon atoms (e.g., phenylthio);
an acyloxy group of 2-18 (preferably 2-8) carbon atoms which may have one or more substituent groups (e.g., acetoxy, ethylcarbonyloxy, cyclohexylcarbonyloxy, benzoyloxy, and chloroacetyloxy);
a sulfonyloxy group of 1-18 (preferably 1-8) carbon atoms which may have one or more substituent groups (e.g., methanesulfonyl);
a carbamoyloxy group of 2-18 (preferably 2-8) carbon atoms which may have one or more substituent groups (e.g., methylcarbamoyloxy and diethylcarbamoyloxy);
an amino group having 0-18 (preferably 0-8) carbon atoms which may have one or more substituent groups (e.g., non-substituted amino, methylamino, dimethylamino, diethylamino, anilino, methoxyphenylamino, chlorophenylamino, morpholino, piperidino, pyrrolidino, pyridylamino, methoxycarbonylamino, n-butoxycarbonylamino, phenoxycarbonylamino, methylcarbamoylamino, phenylcarbamoylamino, ethylthiocarbamoylamino, methylsufamoylamino, phenylsufamoylamino, acetylamino, ethylcarbonylamino, ethylthiocarbonylamino, cyclohexylcarbonylamino, benzoylamino, chloroacetylamino, methanesulfonylamino, and benzenesulfonylamino);
a carbamoyl group of 1-18 (preferably 1-8) carbon atoms which may have one or more substituent groups (e.g., non-substituted carbamoyl, methylcarbamoyl, ethylcarbamoyl, n-butylcarbamoyl, t-butylcarbamoyl, dimethylcarbamoyl, morpholinocarbamoyl, and pyrrolidinocarbamoyl);
a sulfamoyl group having 0-18 (preferably 0-8) carbon atoms which may have one or more substituent groups (e.g., non-substituted sulfamoyl, methylsulfamoyl, and phenylsulfamoyl);
a halogen atom (e.g., fluorine, chlorine, and bromine); hydroxyl group; nitro group; cyano group; carboxyl group; and
a heterocyclic group (oxazole, benzoxazole, thiazole, benzothiazole, imidazole, benzoimidazole, indolenine, pyridine, sulfolane, furan, thiophene, pyrazol, pyrrole, chroman, and coumarin).
Each of the substituent groups represented by A1 and A2 preferably has Hammett""s substituent constant ("sgr"p) of not less than 0.2. The values of Hammett""s substituent constant ("sgr"p) are set forth in, for instance, Chem. Rev., 91, 165(1991). Examples of the particularly preferred substituent groups include cyano group, nitro group, alkoxycabonyl group, acyl group, carbamoyl group, sulfamoyl group, alkylsufonyl group, and arylsulfonyl group. Examples of the preferred substituent groups represented by B1 and B2 include alkyl group, aryl group, alkoxy group and amino group.
Each of the group of atoms [xe2x80x94C(xe2x95x90L1)xe2x80x94(E)xxe2x80x94C(xe2x95x90X1)xe2x80x94] (hereinafter referred to as xe2x80x9cW1xe2x80x9d) connecting to Y1 and the group of atoms [xe2x80x94C(xe2x95x90L5)xe2x80x94(G)yxe2x80x94C(xe2x95x90X2xe2x88x92)xe2x80x94] (hereinafter referred to as xe2x80x9cW2xe2x80x9d) connecting to Z1 forms a conjugated system, and therefore each of the carbon ring or heterocyclic ring constituting W1 and Y1 and that of W2 and Z1 has a resonating structure.
Each of the carbon ring or heterocyclic ring of W1 and Y1 and that of W2 and Z1 is preferably a 4- to 7-membered ring, more preferably a 5- or 6-membered ring. Each ring may form a condensed-ring with other 4- to 7-membered ring and may have substituent groups. Examples of the substituent groups are the same as those described hereinbefore for A1, A2, B1 and B2. Examples of preferred hetero-atoms in the heterocyclic ring include B, N, O, S, Se and Te. Among them, N, O and S are particularly preferred.
Each of the numbers represented by x and y is independently 0 or 1, and preferably both of them are 0.
X1 is xe2x95x90O, xe2x95x90NR or xe2x95x90C(CN)2, and X2 is xe2x80x94O, xe2x80x94NR or xe2x80x94C(CN)2 in which R is a substituent group. Examples of the substituent group R are the same as those described hereinbefore for A1, A2, B1 and B2. Preferred substituent group R is an aryl group, and more preferably phenyl group. Preferred X1 is xe2x95x90O and preferred X2 is xe2x80x94O.
Examples of the carbon ring constituting the set of W1 and Y1 or the set of W2 and Z1 include following rings (in which each of Ra and Rb independently represents hydrogen atom or a substituent group): 
Among the above rings, A-1 and A-2 are preferred.
Examples of the heterocyclic rings consisting of the set of W1 and Y1 or the set of W2 and Z1 include following rings (in which each of Ra, Rb and Rc independently represents hydrogen atom or a substituent group): 
Among the above heterocyclic rings, A-5, A-6 and A-7 are preferred. Each of Ra, Rb and Rc has the same meaning as that described hereinbefore for A1, A2, B1 and B2. Ra, Rb and Rc may be combined to from a saturated or unsaturated carbon ring (e.g., cyclohexyl ring, cyclopentyl ring, cyclohexene ring, and benzene ring), or a saturated or unsaturated heterocyclic ring (e.g., piperidine ring, piperazine ring, morpholino ring, tetrahydrofuran ring, furan ring, thiophene ring, pyridine ring, and pyrazine ring). In that case, the ring may have one or more substituent groups. Examples of the substituent groups are the same as those described hereinbefore for A1, A2, B1 and B2.
Each of L1, L2, L3, L4 and L5 independently represents a methine group which may have one or more substituent groups. Examples of the substituent groups are the same as those described hereinbefore for A1, A2, B1 and B2. Among them, preferred substituent groups are an alkyl group, an aralkyl group, an aryl group, alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a halogen atom, an amino group, a carbamoyl group and a heterocyclic group. The substituent groups may be combined to form a 5- to 7-membered ring (e.g., cyclopentene ring, 1-dimethylaminocyclopentene ring, 1-diphenylaminocyclopentene ring, cyclohexene ring, 1-chlorocyclohexene ring, isophorone ring, 1-morpholinocyclopentene ring and cycloheptene ring).
Preferred combinations of integers of m and n are m=1 and n=1; m=0 and n=2; and m=2 and n=0.
Next, the cation part is described in detail.
The onium ion represented by Mk+ comprises an onium atom which has positive charge and which has no hydrogen atoms thereon. Examples of the onium ions include a quaternary ammonium ion, oxonium ion, sulfonium ion, phosphonium ion, selenonium ion, and iodonium ion. Preferably, Mk+ is not a cyanine dye but a quaternary ammonium ion.
A quaternary ammonium can be obtained by alkylation (Menshutkin reaction), alkenylation, alkynylation or arylation of a tertiary amine (e.g., trimethylamine., triethylamine, tributylamine, triethanolamine, N-methyl-pyrrolidine, N,N-dimethylpiperazine, triethylenediamine, and N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine) or a nitrogen-containing heterocyclic ring (pyridine, picoline, 2,2xe2x80x2-bipyridyl, 4,4xe2x80x2-bipyridyl, 1,10-phenanthroline, quinoline, oxazole, thizole, N-methylimidazole, pyrazine, and tetrazole).
Mk+ preferably is a quaternary ammonium ion comprising a nitrogen-containing heterocyclic ring, and more preferably a quaternary pyridinium ion.
k is an integer of 1 to 10, preferably 1 to 4. More preferably, k is 2.
The most preferred onium ions for Mk+ are ionic compounds having the below-mentioned formula (II) or (III): 
in which each of R1, R2, R5 and R6 independently represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a heterocyclic group; each of R3, R4, R7 and R8 independently represents a substituent group (including substituent atom); or each set of R3 and R4, R5 and R6, R7 and R8, R1 and R3, R2 and R4, R5 and R7 or R6 and R8 can be combined to form a ring; each of q1, q2, r1 and r2 independently represents an integer of 0 to 4; under the condition that there can be different R3, R4, R7 and R8 in the case that q1, q2, r1 and r2 are 2 or more.
The above-mentioned onium ion for Mk+ can be obtained by Menshutkin reaction (described in, for instance, Japanese Patent Provisional Publication 61-148162) or arylation (described in, for instance, Japanese Patent Provisional Publications 51-16675 and H1-96171) of 2,2xe2x80x2-bipyridyl or 4,4xe2x80x2-bipyridyl with a halide having the desired substituent.
The alkyl group preferably used for R1, R2, R5 and R6 is an alkyl group of 1-18 carbon atoms which may have one or more substituent groups, and more preferably an alkyl group of 1-8 carbon atoms which may have one or more substituent groups. Examples of the alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-hexyl, cyclohexyl and cyclopropyl.
Examples of substituent groups for the alkyl groups include:
a halogen atom (e.g., fluorine, chlorine, and bromine);
an alkoxy group of 1-18 (preferably 1-8) carbon atoms which may have one or more substituent groups (e.g., methoxy and ethoxy);
an aryloxy group of 6-10 carbon atoms which may have one or more substituent groups (e.g., phenoxy and p-methoxyphenoxy);
an alkylthio group of 1-18 (preferably 1-8) carbon atoms which may have one or more substituent groups (e.g., methylthio and ethylthio);
an arylthio group of 6-10 carbon atoms which may have one or more substituent groups (e.g., phenylthio);
an acyl group of 2-18 (preferably 2-8) carbon atoms which may have one or more substituent groups (e.g., acetyl and propionyl);
an alkylsulfonyl or arylsulfonyl group of 1-18 (preferably 1-8) carbon atoms which may have one or more substituent groups (e.g., methanesulfonyl and p-toluenesulfonyl);
an acyloxy group of 2-18 (preferably 2-8) carbon atoms which may have one or more substituent groups (e.g., acetoxy and propionyloxy);
an alkoxycarbonyl group of 2-18 (preferably 2-8) carbon atoms which may have one or more substituent groups (e.g., methoxycarbonyl and ethoxycarbonyl);
an alkenyl group of 2-18 (preferably 2-8) carbon atoms which may have one or more substituent groups (e.g., vinyl);
an alkynyl group of 2-18 (preferably 2-8) carbon atoms which may have one or more substituent groups (e.g., ethynyl);
an aryl group of 6-10 carbon atoms which may have one or more substituent groups (e.g., phenyl and naphthyl);
an aryloxycarbonyl group of 7-11 carbon atoms which may have one or more substituent groups (e.g., naphthoxycarbonyl);
an amino group having 0-18 (preferably 0-8) carbon atoms which may have one or more substituent groups (e.g., un-substituted amino, methylamino, dimethylamino, diethylamino, anilino, methoxyphenylamino, chlorophenylamino, morpholino, piperidino, pyrrolidino, pyridylamino, methoxycarbonylamino, n-butoxycarbonylamino, phenoxycarbonylamino, methylcarbamoylamino, ethylthiocarbamoylamino, phenylcarbamoylamino, acetylamino, ethylcarbonylamino, ethylthiocarbonylamino, cyclohexylcarbonylamino, benzoylamino, chloroacetylamino, and methylsulfonylamino);
a carbamoyl group of 1-18 (preferably 1-8) carbon atoms which may have one or more substituent groups (e.g., non-substituted carbamoyl, methylcarbamoyl, ethylcarbamoyl, n-butylcarbamoyl, t-butylcarbamoyl, dimethylcarbamoyl, morpholinocarbamoyl, and pyrrolidinocarbamoyl);
a sulfamoyl group having 0-18 (preferably 0-8) carbon atoms which may have one or more substituent groups (e.g., non-substituted sulfamoyl, methylsulfamoyl, and phenylsulfamoyl);
cyano group; nitro group; carboxyl group; hydroxyl group; and
a heterocyclic group (e.g., oxazole, benzoxazole, thiazole, benzothiazole, imidazole, benzoimidazole, indolenine, pyridine, sulfolane, furan, thiophene, pyrazol, pyrrole, chroman, and coumarin).
The alkenyl group for R1, R2, R5 and R6 preferably is an alkenyl group of 2-18 carbon atoms which may have one or more substituent groups, and more preferably an alkenyl group of 2-8 carbon atoms which may have one or more substituent groups. Examples of the alkenyl groups include vinyl, allyl, 1-propenyl and 1,3-butadienyl.
Examples of substituent groups for the alkenyl groups are the same as those described hereinbefore for alkyl group.
The alkynyl group for R1, R2, R5 and R6 preferably is an alkynyl group of 2-18 carbon atoms which may have one or more substituent groups, and more preferably an alkynyl group of 2-8 carbon atoms which may have one or more substituent groups. Examples of such alkynyl group include ethynyl and 2-propynyl.
Examples of substituent groups for the alkynyl groups are the same as those described hereinbefore for alkyl group.
The aryl group for R1, R2, R5 and R6 preferably is an aryl group of 6-18 carbon atoms which may have one or more substituent groups. Examples of such aryl group include phenyl and naphthyl.
Examples of substituent groups for the aryl groups are the same as those described hereinbefore for alkyl group. Alkyl groups (e.g., methyl and ethyl) are also preferably used as the substituent groups.
Examples of the heterocyclic groups preferably employable for R1, R2, R5 and R6 include oxazole, benzoxazole, thiazole, benzothiazole, imidazole, benzoimidazole, indolenine, pyridine, sulfolane, furan, thiophene, pyrazol, pyrrole, chroman and coumarin.
Each of R3, R4, R7 and R8 has the same meaning as that described hereinbefore for A1, A2, B1 and B2. Examples of the preferred substituent groups of R1, R4, R7 and R8 include a hydrogen atom and an alkyl group. Among them, a hydrogen atom is particularly preferred.
R5 and R6 are preferably combined to form a ring. In such case, the ring preferably has 5 to 7 members, more preferably 6 members. Each of a set of R3 and R4 and a set of R7 and R8 is preferably combined to form a carbon ring or a heterocyclic ring, more preferably a carbon ring. It is particularly preferred that each of the sets be combined with the connected pyridine ring to form a condensed aromatic ring.
In the oxonol compounds of the formulas (IV-1) and (IV-2), A3, A4, B3 and B4; Y2 and Z2; L6, L7, L8, L9 and L10; and m1 and n1 have the same meaning as those of A1, A2, B1 and B2; Y1 and Z1; L1, L2, L3, L4 and L5; and m and n in the formulas (IV-1) and (IV-2), respectively. Consequently, preferred examples of them are the same.
In M2+ of the formulas (V) and (VI), R11, R12, R13, R14, R15, R16, R17 and R18; and q3, r3, q4 and r4 have the same meaning as those of R1, R2, R3, R4, R5, R6, R7 and R8; and q1, r1, q2 and r2 in the formulas (II) and (III), respectively. Consequently, preferred examples of them are the same.
Concrete examples of preferred anion parts of the dye compounds of the formulas (I-1) and (I-2) are given below.
Concrete examples of preferred cation parts of the dye compounds of the formulas (I-1) and (I-2) are given below.
Concrete examples of the compounds preferably employable for the invention are set forth in Table 1. In Table 1, each compound is shown as a combination of the anion part and the cation part. For example, the compound of No. 1 (Compound No. 1) consists of-the anion part of (B-3) and the cation part of (C-1), and the compound of No. 5 (Compound No. 5) consists of the anion part of (B-3) and the cation part of (C-22). Consequently, each of the compounds of No. 1 and No. 5 has the below-mentioned formula: 
The compounds in Table 1 can be illustrated in the same manner as those of No. 1 and No. 5 described above.
The compound represented by the formula (I-1) or (I-2) can be easily prepared by an ion-exchange reaction between the onium salt having the below-mentioned formula (VIII) and a salt of the dye compound having the below-mentioned formula (VII-1) or (VII-2). The dye compound can be used in the form of an alkaline metal salt (e.g.; Li salt, Na salt, and K salt), an ammonium salt (NH4+ salt) or a salt having an organic counter ion such as a triethylammonium salt (Et3NH+ salt) or a tributylammonium salt (Bu3NH+ salt). The ion-exchange reaction can be carried out in water or in an organic solvent (e.g., methanol, ethanol, isopropanol, and dimethylformamide). 
In the above formulas, A5, A6, B5 and B6; Y3 and Z3; L11, L12, L13, L14 and L15; X3 and X4; E1 and G1; m3 and n3; and x1 and y1 are the same meaning as A1, A2, B1 and B2; Y1 and Z1; L1, L2, L3, L4 and L5; X1 and X2; E and G; m and n; and x and y in the formulas (I-1) and (I-2), and Xrxe2x88x92 in the formula (VII) represents an anion, and r represents an integer of not less than 1 (preferably 1 to 4, more preferably 1 or 2). Examples of the anions include halide ions (e.g., Clxe2x88x92, Brxe2x80x94, and Ixe2x88x92), sulfonato ions (CH3SO3xe2x88x92, p-toluenesulfonato ion, and naphthalene-1,5-disulfonato ion), ClO4xe2x88x92, BF4xe2x88x92, and PF6xe2x88x92.
The dye compound represented by the formula (VII-1) or (VII-2) can be prepared by a condensation reaction between the corresponding active methylene compound (e.g., pyrazolone, thiobarbituric acid, barbituric acid, indandione, and hydroxyphenalenone) and the methine source to introduce a methine group or polymethine group into the methine dye. The methine source are described in detail in Japanese Patent Publication Nos. 39-22069, 43-3504, 52-38056, 54-38129, 55-10059, 58-35544; Japanese Patent Provisional Publication Nos. 49-99620, 52-92716, 59-16834, 63-316853, 64-40827; British Patent No. 1133986; U.S. Pat. Nos. 3,247,127, 4,042,397, 4,181,225, 5,213,956 and 5,260,179. Concrete examples of the methine source for introducing of monomethine group include ortho esters (e.g., ethyl orthoformate and ethyl orthoacetate) and N,N-diphenylformamidine hydrochloride. Examples of the methine source for introducing of trimethine chain include trimethoxypropane, 1,1,3,3-tetramethoxypropane and malonaldehydodianyl hydrochloride (and the derivatives of those above described). Examples of the methine source for introducing of pentamethine chain include glutaconaldehydodianyl hydrochloride and 1-(2,4-dinitrophenyl)-pyridiniumchloride (and the derivatives of those above described).
The syntheses of the dye compounds represented by the formula (I-1) or (I-2) are described below.